In the intervening years, a number of friction devices have been developed, for example, Sumitomo friction damper (Aiken and Kelly 1990), energy dissipating restraint (Nims et al.
1993a), and slotted bolted connection energy dissipator (FitzGerald et a1. 1989; Grigorian et aJ. 1993). Typically, these JOURNAL OF ENGINEERING MECHANICS / SEPTEMBER 1997/901 0.36 0.360 O. 350.
-700+----.....--~~==...;..;.;:\-0.36 -350 -700.
-1050H-----,---r----.--........---r---l -0.360 -0.240 -0.120 0.000 0.120 0.240 Deformation Angle (y= AI L) 350 Z~
-w 0 (,) a:
0u. Py - - -350 Pp - - (8) -z ~-w~ ou. (b)
1050.\
FIG. 3. Hysteresis of Triangular Plate Metallic Damper: (a) Experimental (Tsai et al. 1993); (b) Numerical (Dargush and Soong 1995)
Soong (1995) developed an inelastic constitutive model for the material of metallic yield dampers based on a microscopic
mechanistic approach and made some comparison with experimental data for validation of the model, in which the experimental and numerical results of the hysteretic behavior of
a triangular plate metallic damper are shown in Fig. 3. Tsai and Tsai (1995) developed a finite-element formulation for the tapered-plate energy dissipator, and compared it with experimental data, showing that the proposed model effectively predicts the device behavior under wind and earthquake loading. In the development of suitable hysteretic models, there is
an alternative approach, which involves the direct use of experimental data obtained from component testing of the device.
In this approach, the basic form of the hysteretic model
is first selected, and then the model parameters are determined or the relationships between the model parameters and the size and material parameters of the device are established via a curve fitting procedure or some macroscopic mechanical analysis of the device. In using this approach, any appropriate
hysteretic restoring forcing model, such as a bilinear one, suitable for the metal elements may be selected to describe hysteretic behavior of the devices. Ou and Wu (1995), by employing a bilinear model to describe the hysteretic behavior of
X-shaped and triangular plate dampers, established a relationship between the model parameters and the size and material J. Eng. Mech. 1997.123:897-971. Downloaded from ascelibrary.org by Henan University of Technology on 03/05/13. Copyright ASCE. For personal use only; all rights reserved.
FIG. 4. Pall Friction Damper (Pall and Marsh 1982)
FIG. 5. Force-Displacement Response of Pall Friction Device (Flllatrault and Cherry 1987)
needed in adopting one of these models in the response analysis and design of structures with friction dampers. Additionally, long-tenn behavior and durability of these devices, particularly after long periods of inactivity, have not been adequately addressed.
After a hysteretic model is validated for a particular friction damper, it can be readily incorporated into an overall structural analysis. Although some attempts have been made to introduce the concept of equivalent viscous damping [e.g., Scholl
(1993)], in general, a full nonlinear time domain analysis is required. Recent numerical and theoretical investigations show that parameters YSR (ratio of initial slip load to yielding force of corresponding structural story) and SR (ratio of bracing
stiffness to stiffness of corresponding structural story) are the key ones in reducing seismic response (Nims et al. 1993; Scholl 1993). Comparisons made with corresponding unbraced
and conventionally braced frames indicate that friction dampers effectively reduce displacements, while maintaining comparable acceleration levels (Nims et al. 1993b). Based on nonlinear response analysis, the corresponding design procedure
for frictionally damped structures may be proposed. Filiatrault and Cherry (1990) presented a design method based on the
development of design slip-load spectra. This method does not need nonlinear analysis and may serve as a preliminary design step for the structure and its friction devices.
In recent years, there have been several applications of friction dampers aimed at providing enhanced seismic protection
of new and retrofitted structures. This activity is primarily associated with the use of Pall friction devices in Canada, and
Sumitomo friction dampers in Japan. The Pall X-braced friction devices and their variations have been installed in several buildings, some as retrofits and some new facilities (Pall and Pall 1993, 1996). Three building projects in Japan, including the 31-story steel-frame Sonic office building in Omiya City, involving Sumitomo friction dampers, are briefly described in Aiken and Kelly (1990).
A combination mechanism, which incorporates a friction
damping device for control of structural damage due to severe earthquake motion and a viscoelastic damping device for control of low energy excitation, such as wind forces or mild
ground movements, has also been a subject of recent investigations (Tsiatas and Olson 1988; Pong et al. 1994a,b; Tsiatas
and Daly 1994). This mechanism consists of a frictional slider and a viscous damper acting in series. The viscoelastic material dissipates energy induced by mild earthquakes or wind
action. Once the force exceeds a certain value, the frictional mechanism begins to dissipate energy and at the same time preserves the integrity of the damper.
In other developments, Dorka in 1992 developed a bidirectional friction device, consisting of a stack of sliders that are
alternately flat and convex, causing a nearly circular distribution of clamping pressure over the contact area. Pradlwater et al. (1994) analyzed the random response of a two-dimensional (2D) structure with bidirectional friction devices and studied
their effectiveness in response reduction. Additionally, frictional dampers have been used in the study of seismic retrofit
of reinforced concrete structures (Li and Reinhorn 1995). Experimental and analytical results show that they can reduce
inelastic defonnation demands, and moreover, reduce damage quantified by an index monitoring pennanent defonnations. 2.3 Viscoelastic Dampers
The metallic and frictional devices described are primarily intended for seismic application. On the other hand, there is a class of viscoelastic solid materials that can be used to dissipate energy at all defonnation levels. Therefore, viscoelastic
dampers can find applications in both wind and seismic protection. col.
I+t--Iinks 1000 4.45
'0.40 -0.20 0.20 0.40 (In) I!
-10.18 -5.08 5.08 (mm) ·1000 -4.45 -2000 8.90
slip Joint with
friction pad ---t--++++\(8) (b) ,; P
(1bs) (kN) No. of Cycles\
2000 8.110 Excitation Frequency. 0.20Hz
devices provide good perfonnance and their behavior is not
significantly affected by loading amplitude, frequency, or even
the number of loading cycles. The devices differ in their mechanical complexity and the materials used for the sliding surfaces. Recently, a similar type of friction device, the Tekton
friction damper, was tested (Li and Reinhorn 1995). Most friction devices utilize sliding interfaces consisting of steel on
steel, brass on steel, or graphite impregnated bronze on stainless steel. Composition of the interface is of great importance for insuring longevity of operation of the devices. Low carbon alloy steels, for example, corrode and their interface properties will change with time. Moreover, brass or bronze promotes additional corrosion when it is in contact with low carbon. Only steels with high chromium content do not appear to suffer additional corrosion in contact with brass or steel.
At present, most macroscopic hysteretic models for friction dampers are obtained from test data assumed to be Coulomb
friction with a constant coefficient of friction. Some care is 902/ JOURNAL OF ENGINEERING MECHANICS / SEPTEMBER 1997 J. Eng. Mech. 1997.123:897-971. Downloaded from ascelibrary.org by Henan University of Technology on 03/05/13. Copyright ASCE. For personal use only; all rights reserved.